Fermi Definition and 384 Threads

hey guys i just wanted to confirm something; so, for systems of continuous energy states (or small separations of discrete energy states), we can plot a graph like this and call the fermi energy the middle point where Probability=1/2. like this where, if T=0K, the transition from...

I understood that the fermi level is a hypothetical energy level given by the Fermi-Dirac distribution where the probability of finding an electron is exactly 50%. My question is: it always takes (Ec-Ev) energy to excite the electrons in the conduction band in an intrinsic semiconductor or...

All derivations of the Fermidistribution uses a canonical ensemble with a chemical potential, which is the same as to say that the ensemble can exchange particles with a resevoir. But are the derivations still valid for the canonical ensemble with a fixed number of particles and why isn't this...

There seems to be relation between Fermi surfaces and magnetoresistance, but I guess because I don't have a clear picture of fermi surfaces,I have problem understanding this relationship. Also I have heard about open and close fermi surfaces and saturation of magnetoresistance which I can't...

My book notes, that at a given temperature the ratio of the total number of particles in the fermi gas to the total number lying within (ε-kT,ε+kT) is given by: T/TF (1) And that each of these particles has an energy of ≈kT (2). I can't see where this comes from? :S Could anyone explain (1) and (2)?

Does this construction even make sense? By definition it is a surface of constant energy in k-space, so for the free electron it is a sphere. But for metals you have band structure so that a given k-vector can have several different energies associated with it. Which of these are to be chosen?

Homework Statement Regular Doping: Let's say that we want to introduce some electrons into a quantum well, by adding dopant atoms (donors) to the semiconductor. The "regular" way to do this would be to deposit our semiconductor films, first a "barrier" layer with large band gap, then the...

Why is the Fermi level a constant in thermal equilibrium? just like PN diode (P=material 1 ; N=material 2) the fermi levels are the same (Ef1=Ef2) in thermal equilibrium i confused that why there is no energy transfer so that can judge each energy E will obey rate from 1 to 2 ~...

what is fermi energy?

I have posted questions similar to this over the past week, but I have never had a satisfactory answer. It is about the fermi distribution. From hyperphysics: "We picture all the levels up to the Fermi energy as filled, but no particle has a greater energy. This is entirely consistent with the...

Homework Statement In class, we discussed metal quantum dots, and we argued that they’re not so useful for device applications since the separation between energy levels for energies near the Fermi energy is much less than a typical optical photon energy of 2 eV. Let’s consider that...

Homework Statement This question is based on a previous question in the same homework: The Problems deal with Silicon at 300K, using band gap energy Eg = 1.12 eV, electron density of states mass 0.327, hole mass 0.39, electron mobility 0.15 m2/Vs, hole mobility 0.05 m2/Vs and relative...

Homework Statement Consider a pn junction in Si at 300K (other parameters given), with doping NA = 1021/m3 and ND = 1023/m3. Assume all impurities are ionized. On this basis find the Fermi level on each side. From this find the band bending VB and make a sketch of the pn junction. Homework...

Recently a few friends and I were discussing the Fermi sea. One friend made the statement that if you could access the electrons from the Fermi Sea you could use the material you accessed them from as an electron source. Didn't make sense to me but it got me wondering. My question is, What...

Homework Statement 1) This question has to do with pure InAs, with a bandgap 0.33 eV, electron mass 0.02, hole mass 0.41. (a) Evaluate the number of electrons/m3 int he conduction band at 300K. For this purpose you can assume the Fermi Energy is exactly at the center of the energy gap...

Homework Statement problem statement is attached as problem.pdf Homework Equations eqn are given in the pdf file The Attempt at a Solution I have tried in vain to connect Fermi energy with dispersion relation. I just don't have any clue ,I also tried to determine the effective...

Does the (intrinsic) Fermi level of an insulator HAVE to lie very near the middle of the band gap? I know it might deviate slightly if electrons and holes have different effective masses, e.g. in Si. But can it be radically different? For example, are there insulators with 5 eV band gaps that...

The attached jpeg shows Enrico Fermi at the blackboard. There is a geometric drawing and some math I do not understand. Can you point me in the right direction? I have searched for a discussion of what he is presenting but cannot find one. The photo may be familiar because it was...

Hi, everyone. I'm learning basic theories about semiconductors but can't quite understand the concept of Fermi level. is this just a imaginary energy level or true existence? and why Fermi level is close to the conduction band of n-type semiconductor and valence band of p-type semiconductor...

Hello, I have read several articles/websites which talk about modelling white dwarfs, In all of these papers they state that it can be assumed the electrons have temperature zero, i.e. T<<T_fermi. I haven't been able to find a solid explanation of why this is approximation is possible...

Hi! So I'm a bit confused: first off, does Fermi liquid theory have "order". I suppose it depends on how you define order. But in case it does, is it described by symmetry breaking? From what I read, I think it does have order which is not described by symmetry breaking. But then I have...

Homework Statement Some atoms in Cu crystal (Cu has a FCC lattice) are replaced by Zn atoms. Taking into account that Zn is bivalent, while Cu is monovalent, calculate the atomic ratio of Zn to Cu in ZnCu alloy at which the Fermi surface touches the first Brillouin zone faces. Use the...

Homework Statement what is the probability of finding an electron with energy between 5eV and 5.5eV at T=300k, given that the fermi energy of the metal is 4.2 eV. Homework Equations ##P(E,T)dE= \frac{3}{2} E_F^\frac {-3}{2} \frac{E^\frac{1}{2}}{e^\frac{E-E_F}{K_B T}+1}dE## The...

Suppose there is a semiconductor with Fermi energy $E_f$ and that there are $N$ bound electron states. I'd like to know why the mean number of excited electrons takes the form \bar n(T)={N\over \exp\beta(\mu-E_f)+1} where \mu is the chemical potential. ____ I can see that the Fermi...

Hi all, Why do the fermi level for electrons and holes coincide in equilibrium condition and why they separate as quasi fermi levels in non equilibrium situation?

How is it that the calculated Fermi energy of neutrons and protons in a heavy nucleus are different, but it's observed that they have the same energy? And how much is the Coulumb repulsion of the protons play a factor in that?

I know this is true under thermal equilibrium, but I am not sure why. Why can't the Fermi level be a function of position relative to the pn-junction? How does that follow from thermodynamics/statistical mechanics?

The density of states at the fermi energy is given by D(E_F)=(3/2)n/E_F I understand the density of states is the number of states per energy per unity volume, accounting for n/E_F. I don't understand how the 3/2 multiplying factor accounts for the volume?

Hello, I'm studying digital integrated circuits and I'm new to solid state physics. I've studied PN junctions, drift and diffusion currents, now I'm trying to see these subjects in terms of energy bands and I'd really appreciate it you could explain to me a couple concepts. When two materials...

edit* never mind figured it out thanks.

Homework Statement Here g(ε_f) is the density of levels at the Fermi energy and T is the temperature. Calculate the specific heat of the electron gas in potassium (K) treating it as a free gas. For a free gas the density of electrons at ε_f is: g(ε_f)=(3/2)(n/E_f) where n is the electron...

Hello! I have a small question, and I am not sure if I am missing something: Today I glanced at the wikipedia page for Pions, and saw this: Statistics: Bosonic Can anyone explain to me why a quark paired with a anti-quark obey Bose-Einstein Statistics? If quarks obey Fermi-Dirac statistics...

Hey, My question is displayed below I have had a few questions like these and I just want to check my approach is correct, but I'm not sure - I know that the Fermi Energy of Cu is something like 7eV. Now we are told that there are 4 atoms per cube side - meaning 8 atoms but cubic...

Hey I have a question pictured below: I always seem to struggle with questions like these, my understanding is we know the spacing of K-states throughout the lattice is given by \frac{2\pi}{L} Such that the fermi wavevector divided by this spacing and multiplied by 2 due to the fact...

1. How many sands on the earth? 2. Hints: Using the Fermi estimation 3.

i'm reading through halzen and martin's chapter 12 on the weak interaction which they calculate the fermi coupling constant form oxygen beta decay using \Gamma = 1/\tau = G^2E_0^5/30\pi^3 with E_0 = 1.81MeV and \tau log 2 = 71 sec. they get G\approx 10^{-5}/m^2_N. where m_N is the nucleon mass...

I Know that the fermi level in an intrinsic semiconductor is found between the valency level and the conduction level in the energy gap , and I know that also when the semiconductor is doped the fermi level either move toward the conduction band or away from it.But actually I can not get the...

I have searched a lot on the internet for a simple explanation of these two terms. As I have understood these things (quantum physics), after reading from a lot of sources, is that in an atom there are discrete energy levels and electrons occupy the levels according to the least energy of the...

The intrinsic semiconductor Fermi level is the maximum energy level an electron can be in at 0K. Or Fermi level is a level where there is a probability of 50% to find electrons at any temperature. Conduction band is a range of energy where electrons freed from bonding stay. Valence band is...

Homework Statement The density of gold (atomic mass 197) is 19.32 g/cm3. Assuming each gold atom contributes one electron to the free electron Fermi gas, calculate the Fermi energy in eV. Homework Equations Fermi energy is given by: E_F=\frac{h^2}{8m_e} \left( \frac{3N}{\pi V} \right)^{2/3}...

Greetings, I've been doing some literature research and can't seem to find any answers to my question. In an accumulation-mode FET (i.e. only relevant capacitance is that of the gate dielectric), how does one translate the applied gate-voltage to the Fermi energy of the active region? Say we...

Hello! I've just started reading about quantum mechanics, so my question may sound silly. I'm using the book of physics of Paul Tipler. It's says that inside the metals we have a lot of free electrons, like a electrons cloud (like when we learn in the School). These electrons follow the...

Why does the Fermi level level drop with increase in temperature for a n type semiconductor.? What's the basic idea behind Fermi level? How does it get affected by temprature?

Hi everyone, Defined the Fermi Normal Coordinates (which can be seen for example http://relativity.livingreviews.org/open?pubNo=lrr-2011-7&amp;page=articlese10.html" ) is there any heuristic argument to explain why the area element is something proportional to the element of solid angle? I...

Based on Fermi distribution, if there are two electron energy levels with occupation possibility of ¼ and ¾, respectively, calculate energy difference between these two levels.

I read somewhere that the error incurred from approximating the Fermi surface to be a sphere in k-space goes as 1/N where N is the number of electrons. So, N is generally of the order 10^23. I couldn't figure out how they came up with the value. I was trying to say that the actual shape of the...

As we know that the properties of nanoscale material are quite diffrent from the bulk's. But what's the threshold of the size, or what the upper limmit where significant difference can be observed? The De Broglie wavelength or the Fermi wavelength of the electron in material? How to understand that?

The fermi four point interaction (consider its modern version, quark up to down plus electron plus antineutrino) is not renormalisable Then we introduce an intermediate boson W in the middle. Then we give mass to this W using the higgs mechanism. Then we produce the higgs via a fermion...

Homework Statement Graphite has a structure of parallel planes weakly interacting with each others such that for many effects it can be considered as two dimensional. Each plane has a hexagonal (honeycomb) structure with a single C atom by site which gives 1 electron of conduction. Assume that...

As we know, in intrinsic semiconductors the fermi level is halfway between the valence and conduction band. and The fermi level is the level in which the most energetic electron settles at T=0. but my question: How can the fermi level be in a forbidden region in intrinsic semiconductors? or...